The invention is related to a digital telecommunication system with stored program control, and more specifically, to a common channel signaling input/output processing module of such a telecommunications system utilized for inter-office signaling.
The central switching equipment of a digital telecommunications system conventionally is composed of three major sections. Line trunk group units provide interfaces to the transmission paths of the telecommunication system and are, in turn, commonly connected to a central switching network. The core of the central switching system is a central control which governs the operation of the line trunk group units and the central switching network as well. In view of the fact that controlling of the switching process in a larger digital telecommunication network comprises a multiplicity of interrelated control operations, it is conceivable that the switch control has a decentralized structure wherein the central control becomes a master to direct the actions of the subordinate sections which comprise control capabilities designed to perform specialized tasks.
Such a decentralized control concept necessitates quite some exchange of control information conventionally designated as signaling information in both directions between the central control and specialized control units arranged in other sections of the system. One conventional solution to this control data transfer problem is often called "Common Channel Signaling" comprising a communication link between the central control and peripherals separate from individual and temporary information communication links.
Common channel signaling can be of special significance in telecommunication networks constructed of a plurality of central offices interconnected by trunks terminating in line trunk group units of respective ones of the central offices. One trunk of each respective inter-office connection is dedicated to common channel signaling and is associated with a peripheral control unit here designated as signaling link controller. The signaling link controllers SLC itself have information processing capabilities for processing the signaling information on the trunk group level.
More specifically, a central processor system forming the core of a local central control communicates across separate transmission lines with selected ones of the signaling link controllers in order to steer and monitor switching processes involving remote central offices of corresponding design. In fact, this means that a separate input/output transfer subsystem has to be designed for bi-directional transfer of signaling information for this purpose. It may be noted that this information is interpreted as data information within this subsystem in contrast to further control information which specify the control parameters just for performing this specialized signaling information transfer.
One advantage of such a decentralized control is that processing levels are established which are dedicated to limited tasks, and information is processed on these different levels simultaneously. In this manner, the signaling information can be processed easier under real time conditions and enables the switching system to handle a multiplicity of simultaneous operations at a high data rate without loss of voice or data information to be transferred through the switching system. Nevertheless, the processing of signaling information and the transfer of this information in itself requires quite an amount of the capacity of the central control. This aspect of transferring and processing signaling information becomes more and more important with increasing size and complexity of the digital telecommunication system. In other words, the higher the amount of data traffic between the connected central offices, the more desirable it is to dedicate trunks as common signaling channels for accomplishing the data traffic between pairs of such central offices.